1. Field of the Invention
The invention relates to a metering bottle, in particular to a bottle designed to contain a liquid product, equipped with a device for automatic metering of amounts of liquid to be dispensed.
2. Brief Description of Related Art
Numerous dispensers for liquids comprising a metering device are known. There are particular dispensers in which the main reservoir communicates by means of a syphoning device with a dosing chamber. These devices are quite frequently complicated in their use and require, in comparison with standard bottles, additional motions by the user, such as pumping operations. Additionally, they generally comprise a large number of parts, which makes their manufacture relatively complicated.
Metering dispensers of the piston type are also known. These devices contain a receptacle comprising a dispensing opening connected with a movable piston in a chamber with which the receptacle is provided. The piston is designed to cover said dispensing opening after a short lapse of time at the time it is emptied of liquid. When a dose of liquid is to be dispensed, the dispenser is reversed in such a way that its dispensing opening is in the lower position. The product then flows across this opening, whereas the piston progressively descends in the chamber until it covers the dispensing opening of the bottle. Such dispensers are relatively unreliable as far as the amounts of liquid which they allow to be dispensed is concerned. Because the amount of liquid dispensed depends on the pressure exerted by the piston at the time it is emptied, the amount of liquid dispensed is generally dependent upon the amount of liquid contained in the receptacle.
European Patent Application EP 0 274 256 proposes a metering dispenser which permits a solution to this problem as well as obtaining a dose which does not appreciably depend on the state of fullness of the receptacle. The forward movement of the piston in its metering chamber is controlled by the difference of the pressures to which the surfaces of the piston are subjected. This difference is constant regardless of what the amount of liquid in the receptacle due to a particular shaping of the dispensing opening and chamber. Accordingly, the piston of this dispenser can be adapted in a quite exact manner to the chamber in which it slides.
If there is play between the piston and the chamber, the two amounts of liquid each side of the piston are in communication and the pressure differences on the surfaces of the piston are attenuated. If, on the other hand, the dimensions of the piston are slightly larger then the dimensions of the chamber, the downward movement of the piston will be slowed by friction. In both cases, the dose becomes inexact. Because pieces with exact dimensions are rarely obtained when they are molded of plastic material (plastic is the material which is most often used for such storage bottles), the manufacture of this dispenser is difficult due to loose molding tolerances.